We used to be members of the NT, stopped several years ago after witnessing the absurd 'PC' burblings of their leading lights trying to rewrite history, and/or apologise for this country's colonialist past.
Most of the developed countries in Europe some 4 or 5 hundred years ago went round the world exploring, sometimes conquering and colonialising. It's what people did back then, they didn't know any better.
Trying to apologise to visitors that a certain property had a history of family/ies that were associated with such activity is utterly pointless . . . and trying to erase that history because it makes some 'PC' pen-pusher feel better is also pointless. . . .and wildly misleading to younger visitors, whose history 'education' may be in any case lacking due to schooling failures in recent times.
It's like trying to make WW1 & 2 history go away by air-brushing it out of books, doesn't alter that it really did happen.
NB -- for those who haven't heard of it, consider a National Art Pass, we consider it much better value than NT membership now, gets you discounted or free entry into a great many venues?